To update a product price, first click Products in the main navigation, and identify the product.

Click the product name to open the editor.

Click the retailers tab,
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Scroll down to identify the product in need of update.  Click the name to to open the Retailer Product Editor.

Update the price as shown
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And stock status as needed:
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Click Save in the upper right and the price update will be recorded.

Any subsequent updates by a crawler will overwrite any manually updated prices.